This disclosure directs itself to a tone control system for string instruments having a pair of pickup transducer sensors coupled in series that permits selective enabling of a filter coupled to a selected one of the pickup transducer sensors, or selectively coupled to the series combination of pickup transducer sensors, or coupling a filter with a selected frequency response to a pickup transducer sensor. More in particular, the disclosure is directed to a tone control system for string instruments that includes a capacitive filter formed by at least one capacitor and one of a potentiometer or a three position switch. Still further, the disclosure is directed to a tone control system where responsive to selective positioning of the displaceable contact of the potentiometer or switch, the signals output by one of the series coupled pickup transducer sensors is selected to be low pass filtered while the other is provided with a high frequency bypass path (high pass filter) or neither of the pickup transducers are filtered. The disclosure is also directed to a tone control system where responsive to selective positioning of the displaceable contact of the potentiometer or switch, the signals output by one of the series coupled pickup transducer sensors is selected to be low pass filtered while the other is provided with a high frequency bypass path (high pass filter), or the series combination of pickup transducer sensors is selected to be low pass filtered, or neither of the pickup transducer sensors are filtered. The disclosure is further directed to a tone control system where responsive to selective positioning of the displaceable contact of the potentiometer or switch, the signals output by one of the pair of series coupled pickup transducer sensors is coupled to a selected one of a pair of filters, each providing a different filter frequency response, or the signals of both of the pickup transducers are unfiltered.
Electric string instruments, such as electric guitars, electric bases, electric violins, etc., use one or more pickup transducers to convert the vibration of the instrument's strings into electrical impulses. The pickup transducers may use sensors formed by piezoelectric devices, optical devices, microphones or magnetic pickup coils. The most commonly used pickup transducers use the principle of direct electromagnetic induction and utilize pickup coils to detect changes in a magnetic field due to the movements of a string. Magnetic transducers include a plurality of permanent magnets to create the magnetic fields that change in response to the movement of the strings and at least one coil as a sensor to detect the magnetic field changes. Transducers having magnetic sensors being the most common, the pickup transducers are themselves often simply called pickup coils, or simply “pickups.” The signal generated by the pickup transducers is of insufficient strength to directly drive an audio transducer, such as a loudspeaker, so it must be amplified prior to being input to the audio transducer. The output of some types of pickup transducers may be of sufficient strength to drive an audio transducer such as headphones.
Between the neck and bridge portions of a string instrument the amount of string movement of any of the strings varies, with greater movement occurring in proximity to the neck portion as compared with that adjacent to the bridge portion. Thus, the voltages of the fundamental frequency and lower frequency harmonics (overtones) are generated with greater amplitude in the region of the neck transducer relative to that of the bridge transducer and voltages of higher frequency harmonics of greater amplitude and a lower amplitude fundamental frequency are generated in the region of the bridge transducer relative to that of the neck transducer. Because of this difference it is common for modern electric string instruments to use multiple pickups spaced on the instrument's body between the neck and bridge, and combined and/or selected with blend/configuration controls to achieve a particular sound effect, often in the midst of being played by the musician.
All magnetic pickup coils tend to pick up ambient electromagnetic interference (EMI) from electrical power wiring in the vicinity, such as the wiring in a building, due to their natural inductive qualities. The EMI from a 50 or 60 Hz power system can result in a noticeable “hum” in the amplified audio by from the audio transducer, particularly with poorly shielded single-coil pickups. Double-coil “Humbucker” pickups were invented as a way to overcoming the problem of unwanted ambient hum sounds. Humbucker pickups have two sensing coils arranged to be of opposite magnetic and electric polarity so as to produce a differential signal. As ambient electromagnetic noise effect both coils equally and since they are poled oppositely, the noise signals induced in the two coils cancel out. The two sensing coils of a Humbucker are also usually wired in series to give a fuller and stronger sound. Two individual single sensing coil pickup transducers, if properly poled and polarized, can be combined to suppress hum. Here to, by wiring the two individual sensing coils pickup transducers in series produces a fuller and stronger sound.
Networks formed by ganged or individual potentiometers with series coupled capacitors for “treble control” and parallel coupled capacitors for “bass control” have been used for many years. However, such controls do not give the musician the option for a natural unfiltered sound without the use of a switch to bypass the tone control network. Even with the use of such a switch, such prior art systems do not provide the options of selecting which of a pair of single pickup transducers or sensing coils of a Humbucker pickup transducer the filtering is to be applied. Nor do prior art systems provide the ability to select between applying the filtering to one pickup transducer, or Humbucker sensing coil, and the series combination thereof, or selecting between filters of different frequency response to be a applied to one of the pickup transducers, or Humbucker sensing coil. It is therefore an object of the invention disclosed herein to overcome those, and other deficiencies in the prior art.